Nestjs Patterns

NestJS Patterns

Project Structure

src/
├── main.ts                    # Bootstrap
├── app.module.ts              # Root module
├── common/
│   ├── decorators/
│   ├── filters/               # Exception filters
│   ├── guards/                # Auth guards
│   ├── interceptors/          # Logging, transform
│   └── pipes/                 # Validation
└── modules/
    └── users/
        ├── users.module.ts
        ├── users.controller.ts
        ├── users.service.ts
        ├── users.repository.ts
        ├── dto/
        │   ├── create-user.dto.ts
        │   └── update-user.dto.ts
        └── entities/
            └── user.entity.ts

main.ts

import { NestFactory } from '@nestjs/core'
import { ValidationPipe, VersioningType } from '@nestjs/common'
import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger'
import { AppModule } from './app.module'

async function bootstrap() {
  const app = await NestFactory.create(AppModule)

  // Global validation pipe
  app.useGlobalPipes(new ValidationPipe({
    whitelist: true,       // strip unknown fields
    forbidNonWhitelisted: true,
    transform: true,       // auto-cast types
    transformOptions: { enableImplicitConversion: true },
  }))

  // API versioning
  app.enableVersioning({ type: VersioningType.URI, defaultVersion: '1' })

  // Swagger
  const config = new DocumentBuilder()
    .setTitle('API')
    .setVersion('1.0')
    .addBearerAuth()
    .build()
  SwaggerModule.setup('api/docs', app, SwaggerModule.createDocument(app, config))

  app.enableCors({ origin: process.env.CORS_ORIGIN })
  await app.listen(process.env.PORT ?? 3000)
}
bootstrap()

Module

// users/users.module.ts
import { Module } from '@nestjs/common'
import { TypeOrmModule } from '@nestjs/typeorm'
import { UsersController } from './users.controller'
import { UsersService } from './users.service'
import { User } from './entities/user.entity'

@Module({
  imports: [TypeOrmModule.forFeature([User])],
  controllers: [UsersController],
  providers: [UsersService],
  exports: [UsersService],
})
export class UsersModule {}

Controller

// users/users.controller.ts
import { Controller, Get, Post, Patch, Delete, Param, Body, Query, HttpCode, HttpStatus, UseGuards } from '@nestjs/common'
import { ApiTags, ApiBearerAuth, ApiOperation } from '@nestjs/swagger'
import { JwtAuthGuard } from '../common/guards/jwt-auth.guard'
import { UsersService } from './users.service'
import { CreateUserDto } from './dto/create-user.dto'
import { UpdateUserDto } from './dto/update-user.dto'
import { PaginationDto } from '../common/dto/pagination.dto'

@ApiTags('users')
@Controller('users')
export class UsersController {
  constructor(private readonly usersService: UsersService) {}

  @Get()
  @ApiOperation({ summary: 'List users' })
  findAll(@Query() pagination: PaginationDto) {
    return this.usersService.findAll(pagination)
  }

  @Get(':id')
  findOne(@Param('id') id: string) {
    return this.usersService.findOne(id)
  }

  @Post()
  @HttpCode(HttpStatus.CREATED)
  create(@Body() dto: CreateUserDto) {
    return this.usersService.create(dto)
  }

  @Patch(':id')
  @UseGuards(JwtAuthGuard)
  @ApiBearerAuth()
  update(@Param('id') id: string, @Body() dto: UpdateUserDto) {
    return this.usersService.update(id, dto)
  }

  @Delete(':id')
  @UseGuards(JwtAuthGuard)
  @ApiBearerAuth()
  @HttpCode(HttpStatus.NO_CONTENT)
  remove(@Param('id') id: string) {
    return this.usersService.remove(id)
  }
}

Service

// users/users.service.ts
import { Injectable, NotFoundException, ConflictException } from '@nestjs/common'
import { InjectRepository } from '@nestjs/typeorm'
import { Repository } from 'typeorm'
import { User } from './entities/user.entity'
import type { CreateUserDto } from './dto/create-user.dto'
import type { UpdateUserDto } from './dto/update-user.dto'
import type { PaginationDto } from '../common/dto/pagination.dto'

@Injectable()
export class UsersService {
  constructor(
    @InjectRepository(User)
    private readonly userRepo: Repository<User>
  ) {}

  async findAll({ page = 1, limit = 20 }: PaginationDto) {
    const [users, total] = await this.userRepo.findAndCount({
      skip: (page - 1) * limit,
      take: limit,
      order: { createdAt: 'DESC' },
    })
    return { users, total, page, limit }
  }

  async findOne(id: string): Promise<User> {
    const user = await this.userRepo.findOneBy({ id })
    if (!user) throw new NotFoundException(`User ${id} not found`)
    return user
  }

  async create(dto: CreateUserDto): Promise<User> {
    const existing = await this.userRepo.findOneBy({ email: dto.email })
    if (existing) throw new ConflictException('Email already in use')
    const user = this.userRepo.create(dto)
    return this.userRepo.save(user)
  }

  async update(id: string, dto: UpdateUserDto): Promise<User> {
    const user = await this.findOne(id)
    Object.assign(user, dto)
    return this.userRepo.save(user)
  }

  async remove(id: string): Promise<void> {
    const user = await this.findOne(id)
    await this.userRepo.remove(user)
  }
}

DTOs with class-validator

// dto/create-user.dto.ts
import { IsEmail, IsString, MinLength, MaxLength, IsOptional, IsEnum } from 'class-validator'
import { ApiProperty, ApiPropertyOptional } from '@nestjs/swagger'
import { Role } from '../entities/user.entity'

export class CreateUserDto {
  @ApiProperty({ example: 'alice@example.com' })
  @IsEmail()
  email: string

  @ApiProperty({ example: 'Alice' })
  @IsString()
  @MinLength(1)
  @MaxLength(100)
  name: string

  @ApiPropertyOptional({ enum: Role, default: Role.USER })
  @IsOptional()
  @IsEnum(Role)
  role?: Role
}

Guards

// guards/jwt-auth.guard.ts
import { Injectable, UnauthorizedException } from '@nestjs/common'
import { AuthGuard } from '@nestjs/passport'

@Injectable()
export class JwtAuthGuard extends AuthGuard('jwt') {
  handleRequest(err: any, user: any) {
    if (err || !user) throw err || new UnauthorizedException()
    return user
  }
}

Interceptors

// interceptors/transform.interceptor.ts
import { Injectable, NestInterceptor, ExecutionContext, CallHandler } from '@nestjs/common'
import { Observable } from 'rxjs'
import { map } from 'rxjs/operators'

@Injectable()
export class TransformInterceptor<T> implements NestInterceptor<T, { data: T }> {
  intercept(_ctx: ExecutionContext, next: CallHandler): Observable<{ data: T }> {
    return next.handle().pipe(map(data => ({ data })))
  }
}

Exception Filters

// filters/http-exception.filter.ts
import { ExceptionFilter, Catch, ArgumentsHost, HttpException, Logger } from '@nestjs/common'
import type { Request, Response } from 'express'

@Catch(HttpException)
export class HttpExceptionFilter implements ExceptionFilter {
  private logger = new Logger(HttpExceptionFilter.name)

  catch(exception: HttpException, host: ArgumentsHost) {
    const ctx  = host.switchToHttp()
    const res  = ctx.getResponse<Response>()
    const req  = ctx.getRequest<Request>()
    const status = exception.getStatus()

    this.logger.warn(`${req.method} ${req.url} → ${status}`)
    res.status(status).json({
      statusCode: status,
      message: exception.message,
      path: req.url,
      timestamp: new Date().toISOString(),
    })
  }
}